The invention relates to mulch products of the type that are spread on bare soil surfaces, such as landfills and embankments along new highways, to prevent soil erosion and to encourage the growth of ground cover. The invention also relates to processes for making and applying such mulch products.
Highway embankments, landfills and other areas of bare soil are subject to wind and water erosion. They are also unsightly. Hence, it is desirable to establish a ground cover, such as grass, on the soil surface as soon as possible. Unfortunately, in the course of construction or land filling, any top soil is usually stripped away or covered up. The resultant surface soil is barren, formerly subsurface soil lacking in humous and plant nutrients. The quality of such soil can range from very loose sandy soil which retains water very poorly to heavy clay soil which becomes very hard when dry. To counteract these conditions and promote establishment of a ground cover on the barren soil surfaces, a variety of mulches have been proposed.
U.S. Pat. No. 3,210,173 to Mozell proposes application of an asphaltic emulsion containing salts of fatty acids to promote water retention in barren soil. With the rapidly rising costs of petroleum products, this type of mulch is economically impractical. U.S. Pat. No. 3,943,078 to James discloses a related, latex-based product for use in compacting and stablizing soil for roadbeds and the like, rather than for use as a mulch.
Paper pulp and wood cellulose fibers have long been used as a mulch material. These materials are typically sprayed on the soil surface by a hydro-mulching apparatus in the form of a water slurry to which fertilizers, grass seed and a tackifier have been added. The baled material dries to form a thin fibrous convering over the ground which admits rainwater, yet retains the soil against water and wind erosion. A typical mulch product of this type is SILVA fiber manufactured by Weyerhauser Company, Tacoma, Washington. Such material is delivered to the user packed in large compressed bales. The baled material is compact and intertangled, and so must be manually separated before adding to the slurry in the tank of the hydro-mulching equipment. When wetted, this material hardens, making separation both more necessary and more difficult. Despite careful separation, plugging of the equipment by large globs of undispersed fiber is frequent, necessitating disassembly of the pumping apparatus to remove the plug. When the material is applied in slurry form, smaller globs, too small to plug the machine, are ejected as a part of the spray. The material in such globs fails to disperse adequately on the soil surface. Another problem with this type of mulch material is that it tends to absorb large quantities of nitrate materials during decomposition, thus creating a deficiency of this valuable plant nutrient. Substantial quantities of chemical fertilizer must be added to the slurry to compensate for this loss. However, rainfall or irrigation rapidly leaches out the added chemical fertilizer, leaving the plants with little nutrients to rely on after the first surge of growth. Hence, additional fertilizer should be applied within about a year to sustain vigorous plant growth. A further problem is that the availability of paper pulp and wood cellulose has declined in recent years. The cost of mulch materials has correspondingly increased to the point of economic infeasibility.
Other materials that have been used for mulching bare soil surfaces are grass or straw fiber, particularly the grass screenings left after removal of the grass seed. However, grass and straw fibers are very stiff. They do not disperse well on a soil surface and, thus, do not adequately protect the bare soil from wind and water erosion. Substantial quantities of an artificial tackifier--for example, 30 to 40 pounds of Esi-Tak, manufactured by Environmental Stabilizer International, Inc.--should be added to the slurry to adhere the fibers to the soil. Grass and straw mulches also suffer from all of the above-mentioned drawbacks of wood fiber and paper pulp mulch. Grass fiber has also been pelletized, but no improvement in its soil-holding characteristics was noted. Consequently, governmental agencies have widely disapproved grass fiber as an acceptable mulch material for use on embankments along public highways and on other areas of bare soil under their control.
U.S. Pat. No. 3,099,897 discloses a process for mulching with mica. Finely-divided mica platelets are mixed in a water slurry and sprayed on a bare soil surface and to promote moisture retention. However, mica is a nonrenewable mineral resource and is expensive. While the mica does not take nutrients from the soil, it neither adds nutrients nor prevents the leaching out of chemical fertilizers.
Although not pertinent to the problems of mulching bare soil surfaces, several kinds of soil conditioning and fertilizing compositions have been proposed.
U.S. Pat. No. 3,269,824 to Aswell describes wastepaper soil conditioning and fertilizing pellets which are worked into the soil to aerate and lighten the soil, to promote moisture retention and to slowly release nutrients into the soil. The pellets are an extruded or stamped composition of repulped wastepaper, waste paperboard, fresh wood pulp, pulped bagasse, pulped bark or other pulp cellulose to which has been added a variety of plant nutrients. The pellets are tightly compressed to effectuate a timed release of the added nutrients. Accordingly, they are unsuitable for application as a surface mulch. They are too hard to be distributed dry. They do not absorb water quickly enough to disperse and cover a bare soil surface to form an effective protective mulch thereon. They are likewise too hard to be dissolved quickly enough for mixing in a slurry for spray application, and were never intended to be so applied.
U.S. Pat. No. 3,307,934 to Palmer, et al. describes a method of making a granulated peat fertilizer. In this product, the peat is mixed with chemical fertilizer to reduce the tendency of the fertilizer to scorch the plants before dispersing into the soil. The proportion of peat to inorganic salt is in a range of 20%-60% on a dry weight basis. This product is essentially a fertilizer. It does not contain enough peat to act as an effective surface mulch. The peat is provided in only sufficient quantities to act as a buffer for the chemical fertilizer ingredients.
Accordingly, there remains a need for an effective mulch for application in either wet or dry form to bare soil surfaces to prevent erosion, hold moisture in the soil and not deplete the soil of nutrients or, preferably, contribute nutrients to the soil.
In the process of mint oil extraction, considerable quantities of waste products are generated. In the production of peppermint and spearmint oil, mint hay comprising dried, harvested mint plants, is crushed and steamed to release the oils. Once the oils have been extracted, the processor must somehow dispose of the residual, water-sodden mint plant material, known as mint slugs. Conventionally, the mint slugs are either spread on fields and plowed into the soil or are dried and burned. So far as is known, mint slugs have been considered useless once their oil has been extracted. Hence, it would be desirable to alleviate farmers and mint oil producers of the problems of disposal of mint slugs. It would also be desirable to put the mint slugs to productive use.